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Don’t leave your greenhouse standing empty over autumn and winter. The protection it provides will not only help you to keep tender plants frost-free, it will also let you grow hardy crops, such as salads and herbs, all winter.
An unheated greenhouse can keep overnight temperatures as much as 5°C warmer than outside, which will keep plants frost-free in all but the worst of winters. It will also ensure plants stay dry, which greatly aids survival. A dry plant is much less likely to freeze than a damp one. It is often the combination of cold and wet that kills borderline-tender plants outside over winter.
Just make sure your plants get plenty of light, as natural levels are low in winter. Remove any shading material and clean the glass to maximise the available light.
The following plants are all ideal for growing in a cold greenhouse through autumn and winter.
Try hardy lettuces, such as ‘Salad Bowl’, as well as rocket, pak choi, mizuna, lamb’s lettuce and spinach. Sow in trays or pots of compost, then plant seedlings into large containers, border soil or this year’s old growing bags.
Pot up chives, parsley and mint in autumn and bring them into the greenhouse, where they’ll continue growing all winter. It's worth planting up several pots of each, so you can harvest them in succession for a continuous supply.
Many summer bedding plants can be overwintered in a cold greenhouse, including fuchsias, marguerites and pelargoniums. The extra protection provided will keep these plants alive, but take care not to overwater them.
Lift a crown in autumn and leave on the soil surface – it's hardy enough to survive being frosted. Bring the crown into the greenhouse in late December and cover with a large tub to exclude light. Pick the stems when 30cm long.
Prone to leaf-curl fungus, the foliage of both plants can be kept disease-free if planted in the border of a cold greenhouse in autumn, or grown in pots that are kept under cover between October and late March.
Although most are hardy, alpines benefit from protection during wet weather, as this spoils the flowers and encourages rotting. Bring plants indoors over winter, then move them outside again once the flowers fade.
Pot up tulips, daffodils and hyacinths in autumn and stand them outside for six weeks. Then bring into the greenhouse to encourage early blooms. When buds appear, take the pots into the house and enjoy the display.
lescala 19/10/2012 at 18:24
I have a plastic greenhouse. Will that keep plants etc protected from frost? Sue
sotongeoff 19/10/2012 at 18:27
lescala wrote (see)
Highly unlikely-not without some extra protection,insulation or heating.
Lilylouise 19/10/2012 at 19:14
What plants are you hoping to protect lescala ?
Pam LL x
hollie hock 19/10/2012 at 19:57
It really does depend on the plants, it's unlikely that tender non hardy plants will make it through any sort of unheated greenhouse through the winter. When over wintering plants you also have to think about your location and what sorts of Winter you can expect
